Multi rblx thing

Ok so I downloaded the multi rblx thing and did everything like I use to do and for some reason it didnt work. I opened it before roblox and logged into my main then joined a game then logged out of main went into my alt acc joined my main and when my alt joined my main closed and I dont know why because ive seen people and youtubers and it works for them, so i've been trying to figure out why its not working.